Fabrication of Mechanically-Robust Cu Films on Flexible Substrates Using Electron Beam Irradiation

A primary challenge for a designing of flexible and stretchable devices is to prevent the mechanical failure of the metallic electrodes and interconnects integrated on polymeric substrates under mechanical deformation, e.g., tension, compression, and bending. Herein, we firstly demonstrated that the irradiation of e-beam could significantly improve the mechanical stability of Cu film deposited on polyimide (PI) substrate. The 100nm thick Cu film was deposited on the PI substrate by thermal evaporation and then directly irradiated by low power of e-beam using the scanning electron microscope (SEM). When we applied a tensile strain of 30 %, the e-beam irradiated Cu film on the PI substrate did not exhibit any significant damage, whereas the pristine Cu films did form channeling cracks or delamination. Furthermore, the resistance of the irradiated Cu film increases much less than that of pristine Cu film at a strain of 30%. The mechanical stability was possibly improved due to the enhancement of adhesion between Cu and PI by e-beam irradiation. We believe that our new finding will open up a new facile method to enhance the reliability of metal interconnects and electrodes in the flexible and stretchable devices.